2012 IR&D Annual Report

Development and Validation of a Shock Tube Apparatus for High-Fidelity Blast Wave Generation, 18-R8132

Principal Investigators
James Mathis
Walt Gray
Thomas Z. Moore
Larry Goland
Trenton Kirchdoerfer

Inclusive Dates:  01/01/10 – 12/31/11

Background — SwRI has identified blast and blunt impact trauma as an emerging market opportunity well suited to its impact and blast physics expertise. SwRI's current blast loading method of using high explosives presents limitations in experimental fidelity and repeatability and has been met with skepticism by proposal reviewers in the medical community. Although trauma research using explosives is still being conducted, the shock tube method has become the de facto standard. Large shock tube apparatuses are currently under development at other organizations conducting blast trauma research. Without such a device, a gap will soon appear in SwRI's research capabilities that may severely limit its ability to maintain a viable research program in blast trauma. For that reason, researchers proposed to design and build a high-fidelity shock tube apparatus.

Approach — The goal was to design and develop a shock tube test apparatus with sufficient flexibility to achieve the range of shock pressure conditions required to study a broad spectrum of blast trauma mechanisms. The apparatus that was developed is unique in that it includes an adjustable length high-pressure gas reservoir section allowing for independently tailoring the shock peak pressure and pulse width (impulse) with a single device. In current shock tubes, the peak pressure and impulse are coupled, and tailoring usually requires significant hardware changes. This approach had not been attempted before and required a significant research and design effort.

SwRI-designed shock tube system.
SwRI-designed shock tube system.

Accomplishments — A new shock tube system was designed and fabricated, see photo above. The system consists of four primary components: the adjustable length high-pressure driver section, a dual burst diaphragm section, a modular expansion section, and a test section. The driver section consists of a 4.9-inch internal diameter tube rated at 6,000 psi. The adjustable length is achieved by sliding a movable piston in the tube bore to the desired location along the tube's length. This effectively changes the length of the driver section without having to change hardware. The piston location is infinitely adjustable using a specially designed system. The diaphragm section is a dual-diaphragm design allowing for more precise control over shock tube firing, and allowing higher driver load pressures to be obtained. The internal diaphragm holder can be quickly accessed by removing a single clamp device and moving the entire driver section away via a roller system. The test section currently consists of a 36-inch diameter, 12-foot long pipe. Through testing, the system has been validated to achieve shock pressures up to 10 psi, and durations up to 10 milliseconds. Much higher shock pressures can be achieved by reducing the diameter of the test section and increasing driver fill pressure. The modular design of the expansion section will allow for various test sections to be easily installed. Along with the mechanical design of the system, a complete electronic control system was developed and installed. The system consists of a control console with various pressure readouts and controls that actuate the high speed valves used to fill and fire the shock tube.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.